Embodiments of the disclosed technology relate to a color filter substrate and a liquid crystal display.
Thin film transistor liquid crystal displays (TFT-LCD) have become a dominant kind of flat plate displays in the market due to the advantages of low power consumption, good portability, various applications, high quality, and so on.
At present, a thin film transistor liquid crystal display is formed by injecting liquid crystal material between an array substrate and a color filter substrate after assembling the array substrate and the color filter substrate together. The orientation of the liquid crystal material is controlled by applying voltages on the electrodes on the array substrate and the color filter substrate to form an electric field. The optical characteristics of liquid crystal molecules, such as optical anisotropy, birefringence effect, etc., are utilized to control the luminous flux through the liquid crystal material, thus desired patterns can be displayed on the display panel. Since the cell gap of a liquid crystal cell formed by assembling an array substrate and a color filter substrate together affects the luminous flux through the liquid crystal cell directly, maintaining the cell gap of the liquid crystal cell plays a significant role in improving display uniformity of liquid crystal displays, optimizing display performance, etc.
In order to maintain the uniformity of the cell gap of a liquid crystal cell throughout a liquid crystal display, spacers with certain thickness are conventionally provided between the array substrate and the color filter substrate of the liquid crystal display. Spacers can have two types. One process is to spread ball spacers (BSs) of an uniform size on the array substrate or the color filter substrate by spraying during an assemble process, and the ball spacers of an uniform size are used to maintain the uniformity of the cell gap of the formed liquid crystal cell.
The advantages of this method lie in that ball spacers have good elasticity, are of a low price, and can be applied in a simple process. However, during the spraying process, the number and positions of ball spacers are difficult to control, and ball spacers are easy to aggregate, which may decrease contrast ratio of liquid crystal displays. Thus this method is mainly applied to LCDs for which high display performance are not required.
The other one is to form post spacers (PSs) on the color filter substrate which has been prepared with a black matrix, a color filter layer, and a common electrode layer; PSs are formed as projections in columns on the color filter substrate with a photolithography process by using a mask, and are used to maintain the cell gap of the later formed liquid crystal cell. Because the position, height, appearance of post spacers can be precisely controlled in the photolithography process, the liquid crystal displays using post spacers have significant advance in display performance as compared with the liquid crystal displays using ball spacers.
Presently, in the preparation process of the color filter substrates of TFT-LCDs with post spacers to support and maintain the liquid crystal cell gap, typically a photoresist lithography process is used according to the production design requirements to conduct a photolithography process on a black matrix layer, a color filter layer, and a post spacer layer to obtain the required layer structure. That is, the different kinds of photoresist, which include pigments, small molecule acrylic monomers with multiple functional groups (or other oligomers), ultraviolet light aggregation initiator, organic solvent, pigment dispersing agent and additives for improving coating performance, are used as the materials for forming the black matrix layer, the color filter layer, and the post spacer layer,
In order to enhance the color purity in pixels, a black matrix (BM) for shielding light is typically formed with photoresist filled with carbon. Further, in order to prevent light leakage, the black matrix is generally formed below the boundary between the color filter units of different colors; the color filter units (color pixels) typically are formed with photoresist respectively filled with red (R) pigment, green (G) pigment or blue (B) pigment. Post spacers are generally formed with photoresist of good developing property, high mechanical hardness and strong adhesiveness. In general, the various kinds of photoresist used for forming a color filter substrate are negative types of photoresist. As shown in FIG. 1, in preparing a color filter substrate, firstly a black matrix photoresist layer 5 is deposited on a glass substrate 1 as a base substrate, dried and exposed with ultra violet (UV) light by using a mask, and then subject to a development with a developing solution to remove the unexposed portion after drying and exposure; a black matrix photoresist pattern opposite to the mask pattern is left on the substrate. Subsequently, a red pixel photoresist layer 6, a green pixel photoresist layer 7 and a blue pixel photoresist layer 8 are respectively formed on the glass substrate 1 formed with the black matrix photoresist pattern, and similarly, each kind of photoresist of different color is respectively dried, exposed with a mask, and developed with a developing solution to remove the unexposed portion to obtain color pixels; the color pixel photoresist patterns opposite to the mask patterns for the color pixels of different colors. A common electrode layer 9 is formed on the glass substrate 1 described; then a post spacer layer 10 is formed, dried, exposed with a mask and then developed with a developing solution to remove unexposed portion, and post projections used as post spacers for supporting and maintain the liquid crystal cell gap are formed. Finally, a liquid crystal molecule alignment layer 11 is applied the surface on the glass substrate 1 as described above and treated, and the preparation of the color filter substrate is completed here. The formed structure of color filter substrate is shown in FIG. 1.
In the color filter substrate formed in the above method, since the bonding force between the post spacers 10 and the underlying common electrode layer 9 is weak, it is easily for the post spacers 10 to undergo parallel offset under external pressure, resulting in the change of the cell gap of the formed liquid crystal cell, such that the adverse phenomena of display nonuniformity of the liquid crystal display, light leakage and touch mura (brightness nonuniformity due to the nonuniformity of the liquid crystal cell gap under an external force) are invoked, which affects the display performance and compression resistance performance of the liquid crystal display.